In the art of paper making, the machines employed therefor often comprise endless revolving screen-like belts. It has been discovered that the quality of the paper, cardboard or the like, produced by such machines employing endless revolving screen belts is often impaired due to fouling of the screen belts by impurities. This problem has, generally, been realized as by European Patent Application No. 0053316 filed Nov. 14, 1981, and having a Date of Publication of June 9, 1982.
More particularly, because of regulations relating to environmental protection, the paper making machines, at least in the most part, must employ a closed water circulation and dilution cycle. As a result, the relative amount of impurities in the process water, employed in the paper making process, increases and such impurities deposit upon, among other things, the screen belts. Further, there is an increasing use of recovered or used paper in the production of various grades of paper and such used paper often includes a relatively great amount of impurities which are relatively sticky and may comprise, for example, coloring pigments, latex, resins, bitumen, etc. Also, instead of forming the screen belts from metal wire, as for example phosphor bronze wires, there is an increasing trend to forming the screen belts from wires of synthetic (plastic) material such as, for example, polyester.
The use of screen belts comprised of plastic (synthetic) material creates or at least intensifies the problem of deposits of impurities. That is, experience has shown that the impurities within the process water adhere more strongly to screen belts comprised of plastic material than to metallic screen belts.
Said European Patent Application No. 0053316 has proposed various devices in an attempt to successfully clean the deposited impurities from the screen belts. One of the devices proposed by said European Patent Application No. 0053316 comprises a drum type rotary brush situated as to have its axis of rotation transverse of the running direction of the screen belt and positioned as to have the brush portion thereof in continuous contact with screen belt. As illustrated in FIG. 2 of said Application No. 0053316, the drum type rotary brush 9 is located as to always be at the returning portion of the screen belt which is already free of or separated from the paper or fibre web. Said FIG. 2 depicts, in a fragmentary view, a usual Fourdrinier paper making machine in which, as is known in the art, the fibre or paper web is formed on the top side of the upper screen belt section (not shown in said FIG. 2). Below such paper web-forming zone, the section of screen belt is free of the paper web and travels back as generally indicated by the arrow in said FIG. 2, to what may be considered a starting area for the further continuous forming of the paper web. Because of this, the rotary brush 9 in said FIG. 2 is applied to the returning screen belt 1 from below the screen belt. By so doing such impurities as are removed by said rotary brush 9 can fall into the catch basin or trough 4.
One of the disadvantages of the structure disclosed in FIG. 2 of said Application No. 0053316 is that the rotary brush 9 cannot be employed for cleaning a top or upper screen belt of a double-screen type paper making machine or, if so employed, can be employed only with great difficulties. In such situations it becomes necessary to apply said rotary brush 9 against the returning screen belt section from above such returning screen section.
Further, said Application No. 0053316 fails to provide any information, or even a hint, as to the material which could or should be used for the forming of the bristles of the rotary brush 9. This, therefore, makes it doubtful as to whether the said rotary brush 9 is even capable of removing, in sufficient quantities, impurities from the screen belt.
Accordingly, the invention as herein disclosed and described is primarily directed to the solution of such and other related and attendant problems of the prior art as well as to provide apparatus, for cleaning paper making machine screen belts, which is sufficiently effective even if sticky impurities are abundant.